This invention relates to a process for preparing glass fibers and particularly to the application of a size to continuous filament glass fiber strand during the formation of the strand.
In the production of continuous filament glass fiber strands, a number of individual glass filaments are drawn from an electrically heated platinum alloy bushing containing a molten supply of the glass. The glass passes through tipped orifices in the bottom of the bushing and forms inverted cones of glass at the ends of the tips. Individual filaments are drawn from the cones of glass at a high rate of speed, i.e., 5,000 to 20,000 feet per minute and are grouped into a strand as they pass over a suitable guide. The strand is thereafter wound on a rapidly rotating forming package.
There is no twist in the strand as it is formed and an aqueous size composed of a dispersion of a binder, a lubricant such as detrinized corn starch and a vegetable oil is applied to the individual filaments prior to the time they are grouped into the strand and wound on the forming tube. In order to bond the filaments together and maintain the integrity of the strand, the forming size is deposited on the filaments to provide a level of forming size solids of about 0.7 to about 2 percent by weight based on the weight of the glass. The strand is wound on the tube with a slight traverse so that succeeding turns cross each other at an angle, rather than being parallel to each other so that the strand can be more easily removed from the tube.
A typical glass fiber sizing composition is disclosed in U.S. Pat. No. 3,227,192 which is a sizing composition used for sizing glass fibers which are to be subsequently woven into cloth. Usually, after the forming package is wound, it is placed in an oven to dry or allowed to air dry to reduce the moisture content thereof so that the strand on the forming package can be removed therefrom. After the forming package is dried, the strand is unwound onto a bobbin, the forming package and the bobbin being mounted on a twist frame. During the unwinding and rewinding step, a twist is imparted into the strand which provides integrity for subsequent processing.
When the twisted strand or yarn is to be used for textile applications as previously described, two standard processes are employed to prepare the yarn. A plurality of bobbins are mounted on racks. The end of each bobbin is threaded through a tensioning disc and through a plurality of guide eyes, over a separating comb and onto a beam which is a large cylinder. The plurality of yarn ends are wound on this beam in parallel. This process is known as beaming. The yarn on the beam is used for the warp of a textile glass fabric.
The weft of the textile fabric which is woven generally perpendicularly into parallel twisted strands coming off the beam is supplied by a quill mounted on an apparatus which weaves the weft yarn into the warp yarn. The quill is a spool of small diameter which has the yarn thereon supplied by a bobbin produced as previously described.
After the fabric is woven, it is heat cleaned to remove the size and set the fibers in the fabric. This heating is conducted at a temperature of about 1200.degree. to 1400.degree. F. for 30 to 40 seconds and is sufficient to volatilize the solids and remove them from the fabric and to soften the glass fibers in the fabric to set them in their new position. This process is described in greater detail in U.S. Pat. No. 2,845,364.
Because the weft and warp of the fabric are composed of twisted strand or yarn, the filaments are compressed into the yarn by the twist. Thus, it is necessary to use a plurality of these strands or yarn ends per square inch to have an adequate fill to produce an acceptable fabric. It has been desired by the manufacturers of fabrics to have yarn having no twist so that after heat treatment the single filaments would dissociate from their compacted form and provide increased filling characteristics thus reducing the amount of glass necessary to produce an acceptable fabric. However, yarn without twist has great difficulty in undergoing especially the quilling operation without breaking or fuzzing because once the single filament breaks, it has a tendency to strip away from the strand thus forming fuzz balls and lint. A further advantage of utilizing a yarn without twist in weaving applications is that the yarn can be pulled directly from the inside of the forming package and wound on quills thereby avoiding the additional steps of transferring the yarn from the forming package to the bobbin. However, problems have been encountered in pulling the yarn from the forming package to the bobbin because the strands have a tendency to adhere to each other. Thus, when a package is end found, e.g., a single strand is pulled from the center of a forming package and unwinding is begun. During the pulling while being unwound the strand coheres to other portions of the strand and a large tangle is pulled from the center of the forming package, thus causing a shutdown of the winding operation of the quills.